The present invention relates to medical and surgical apparatus and more particularly to the monitoring of a patient having open-heart surgery by EEG (electroencephalographic) apparatus.
Generally, a carido-pulmonary bypass machine is used in open-heart surgery. A "cardio-pulmonary bypass", i.e., a heart-lung machine, is a mechanical device that assumes the functions of the heart and the lungs for the generally one to four hours of the open-heart surgery. It is a pump and oxygenator which supplies oxygenated blood while the heart is stopped and excluded from circulation. A typical open-heart surgical procedure would be the replacement of the patient's aortic valve, which guards the exit of the left ventricle (cardiac valvular replacement). Due to stenosis (constriction of the valve) it may be repaired or replaced with a plastic, metal, or pig-heart valve.
The medical literature has recognized that cerebral disorders (damage to the central nervous system CNS) may result from open-heart surgical procedures. The studies have indicated that the effect of the disturbed blood flow or metabolism of the brain which may occur during such open-heart surgery may be detected by comparing the patient's EEG (electroencephalographic) examination made before the operation with the EEG examination conducted after the operation. See Sotaniemi et al "Quantitative EEG As A Measure Of Cerebral Dysfunction Before And After Open-Heart Surgery", Electroencephalography and Clinical Neurophysiology, 1980, 50:81-95.
The number of open-heart surgical procedures has risen dramatically in recent years and it is presently estimated that more than 100,000 of such operations may be performed each year. Studies have also indicated that the heart valve replacement operation, which is a widely used open-heart surgical operation, has a comparatively beneficial effect on long-term patient life compared with alternative procedures such as drug regimes. Coronary artery bypass operations, while not yet demonstrated to increase longevity, often improve the quality of the life by decreasing angina pains and limitations on physical activity. Such surgery is being performed at a steadily rising rate.
The present invention is based upon recent findings that certain brain wave information, which may be obtained and specially processed during the open-heart surgical operation, provides a sensitive indication of the progress of the operation and whether remedial steps are immediately required. More specifically, the brain wave information which may be obtained and analyzed simultaneously and on-line with the open-heart operative procedure may be used as an indication of whether the blood flow from the heart-lung machine should be increased or decreased, or whether other measures should be taken to prevent damage to the brain.
Generally, during an open-heart operation it is necessary to decrease the artificial heart pump pressure in order to sew connections to the valves and blood vessels. It is critical, however, that the blood pressure not drop so far, or for such a prolonged period of time, as to bring on cerebral disorder because of lack of oxygen to the brain or disturbances in the brain metabolism. Monitoring of the brain waves during the operation may provide a sensitive indication of the required blood flow so that it does not drop below the critical amount for the critical time period. This is a complicated matter since the blood flow requirement of each individual varies depending upon his or her weight, age, physical condition and metabolism. What may be a sufficient blood flow during open-heart surgery for one patient may be insufficient for the next.